1. Field of the Invention
The present invention relates to a vehicle navigation apparatus and a navigation information displaying method and program. More particularly, the invention relates to vehicle navigation technology that updates a database by receiving difference data.
2. Description of the Related Art
Conventionally, a database for navigation stores map information for use in a vehicle navigation apparatus in a recording medium such as a CD-ROM or a DVD, which is commercially available. A user purchases and uses a recording medium that stores the navigation database, thereby updating a database already installed in his/her own vehicle navigation apparatus. In particular, the updating state of POI (Point of Interest) data, which is included in the map information, concerning different categories such as a shop, bank, gas station, restaurant, hotel, or parking lot, can merely be confirmed by a version value indicative of update information about the recording medium.
Recently, an economical method of updating method of a database in a vehicle navigation apparatus has become mainstream. This method calls for reading difference POI data from a recording medium, which stores therein only the updated difference POI data selected from the whole navigation database. FIG. 12 shows general transmission of difference POI data. As shown in the figure, a database transmission base station 100 transmits difference POI data stored in a database 101 on the database transmission base. Services to transmit or send the difference POI data to a vehicle navigation unit 300 mounted on a vehicle, employing different transmission methods have been proposed. In one transmission method, a digital satellite broadcast is used to transmit the difference POI data from the base station 100 to the navigation unit 300 via a satellite 200. In another method, the transmission of the difference POI data from the base station 100 is conducted using a digital ground wave broadcast or a FM multiplex broadcast.
In the above methods shown in FIG. 12, because all POI difference data for wide areas is to be updated, enormous amounts of data have to be received, thus taking a long time to finish downloading at a time. For example, when POI data to be updated in U.S.A. during one year is updated by using the XM satellite radio, it will take 100 hours. Further, one third of the whole POI data is updated every year. In such a situation, downloading of the data at a time is practically impossible. In consideration of accidentally unread data and the like, if the satellite radio is used for practice, it will take much more time than the downloading time. Even though POI difference data is read from a low-priced recording medium, which stores therein the only POI difference data, to cause a database to be updated, the time lag between updating time of the database and purchase time of the medium occurs without exception.
Thus, users normally utilize databases which are not completely updated, so that search processing is performed as one of navigation functions based on the databases at the timing of not-completed updating.
When using a database that is not completely updated, if data including POI data obtained from search processing has already been updated, it is the latest. However, if it is not updated yet, the data has the old contents. This makes it impossible for the user to judge or determine whether the data obtained from the search processing has the latest contents or not, disadvantageously leading to poor reliability in a navigation apparatus.